1. Technical Field of the Invention
The present invention relates to the synthesis of hydrocarbon compounds which are fluorinated on a carbon atom of an xe2x80x9calkylxe2x80x9d moiety thereof via exchange between a halogen atom having an atomic number greater than fluorine, employing a fluorine-containing reactant which is at least partially in the form of a complex salt.
This invention more especially relates to a process for the preparation of fluorocompounds that are fluorinated on a carbon atom bearing substituent groups which are electron-withdrawing (or attracting) by means of an inductive effect.
2. Description of the Prior Art
Fluorocompounds are characteristically difficult to prepare. The reactivity of fluorine is such that it is difficult, or even impossible, to directly prepare fluoro derivatives.
One of the most commonly used techniques for preparing fluoro derivatives entails reacting a halogen compound, generally a chloro derivative, and exchanging the halogen with an inorganic fluorocompound, generally an alkali metal fluoride, typically of high atomic weight.
In general, the fluoride employed is potassium fluoride, which provides a satisfactory economic compromise.
Under these conditions, many processes such as, for example, those described in French Certificate of Addition No. 2,353,516 and in the article Chem. Ind., 56 (1978), have been carried out industrially to produce aryl fluorides, onto the aryl moieties of which electron-withdrawing groups are grafted.
Except in the instances where the substrate is particularly suitable for this type of synthesis, this technique presents drawbacks, the principal ones of which are those analyzed below.
The subject reaction requires reactants such as alkali metal fluorides, for example potassium fluoride, which are relatively expensive vis-a-vis the technical specifications they must satisfy in order to be suitable for this type of synthesis; they must be very pure, dry and in a suitable physical state.
In addition, this reaction is not operative for an entire class of compounds, in particular those bearing substituents on the halophoric carbon atom (namely, on the carbon atom bearing the halogen or halogens destined to be exchanged with fluorine).
Reactants such as hydrofluoric acid in liquid form, or diluted with dipolar aprotic solvents, are also used. However, hydrofluoric acid is too powerful or harsh a reactant and often results in unwanted polymerization reactions or in tars.
In this event, and especially in the case where it is desired to obtain derivatives fluorinated on a carbon atom of an alkyl radical (including aralkyl) rendered electron-deficient by the presence of electron-withdrawing groups, this art is faced with an alternative which is not encouraging; either very harsh conditions are selected, and tars are especially obtained, or mild reaction conditions are adopted and, in the best of scenarios, the substrate is unchanged. Lastly, the literature describes exchanges carried out utilizing hydrofluoric acid salt reactants in the presence of heavy elements in oxide or fluoride form. Among the elements thus used, antimony and heavy metals such as silver and quicksilver (mercury) are exemplary.
Another disadvantage is the selectivity of the reaction: when there are more than one halogen to be exchanged on the same carbon atom, it is often difficult to exchange less than all of same.
Accordingly, a major object of the present invention is the provision of an improved exchange reaction between, on the one hand, heavy halogen atoms such as chlorine and, on the other, fluorine, while significantly enhancing the specificity of the reaction.
Another object of the present invention is the provision of an improved exchange reaction between the heavy halogens such as chlorine and fluorine, carried out under particularly mild reaction conditions.
Yet another object of this invention is the provision of an improved such process which permits utilizing a source of fluoride whose morphology is less critical.
Still another object of this invention is the provision of an improved such process which permits exchange of only one out of two or three possible halogen atoms.
And yet another object of the present invention is the provision of an improved such process which permits exchange of only two out of three possible halogen atoms.
Another object of this invention is the provision of an improved such process which permits exchange of molecules or atoms to obtain carbon atoms which bear only one fluorine atom simultaneously with one or two other halogen atoms different from fluorine.
Yet another object of the present invention is the provision of an improved such process which permits exchange of molecules or atoms to obtain carbon atoms which bear only two fluorine atoms simultaneously with one other halogen atom which is different from fluorine.
Yet another object of this invention is the provision of an improved such process which avoids the use of a large amount of metals considered to be expensive or toxic, such as mercury and/or silver.
Still another object of this invention is the provision of an improved such process which permits reducing the amounts of metals considered to be expensive or toxic, such as mercury and/or silver, such that the molar ratio between the metal and the substrate whose halogen atoms are to be exchanged is at a value at most equal to 0.5, advantageously at most 0.2, preferably at most 0.1.
And another object of the present invention is the provision of an improved such process which permits avoiding entirely the use of metals considered to be expensive or toxic, such as mercury and/or silver, such as not to add to the reaction mixture any of the elements indicated above; in other words, such that the concentrations of each of said metals do not exceed values of 10xe2x88x923 M, advantageously 10xe2x88x924 M, preferably 10xe2x88x925 M.
Briefly, the present invention features a process for the synthesis of fluorocarbon compounds, comprising reacting a substrate containing at least one sp3-hybridized halophoric carbon atom bearing at least two halogen atom substituents, at least one of which is a halogen atom having an atomic number greater than that of fluorine, said at least one halophoric carbon atom being bonded to at least one chalcogen, with at least one reactant which comprises the combination of a Bronstedt base with a defined amount n of hydrofluoric acid, n being at least equal to 3 and at most equal to 20, preferably at most 10.
More particularly according to the present invention, it has now been determined that certain carbon atoms bearing groups which are electron-withdrawing by an inductive effect are capable of reacting with a reactant of the above type, on condition that at least one of the electron-withdrawing groups is a chalcogen.
The reaction temperature ranges from the melting point of the reaction mixture to its decomposition or boiling point, generally from 0xc2x0 C. to 150xc2x0 C., advantageously from 20xc2x0 to 100xc2x0 C.
The subject process is advantageously carried out at atmospheric pressure, but it can be conducted at pressures of up to 20 105 pascals
Exemplary preferred bases include those which are trivalent hydrocarbon derivatives of elements of column VB, advantageously from a period ranking at least equal to the second and generally less than the sixth, of the Periodic Table of the Elements (supplement to the Bulletin de la Socixc3xa9txc3xa9 Chimique de France, No. 1, January 1966). Other than those described below, exemplary such compounds are trivalent derivatives, which, when they are trisubstituted, are in fact pnictines, these pnictines being more fully described below.
Among said hydrocarbon derivatives of the elements of column V, preferred are those which are derived from hydrogen pnictides by total or partial substitution of the hydrogen with hydrocarbon residues, which may be bonded to the atom from column VB via a double bond (as in the imines), or a triple bond (as in the nitrites).
However, the hydrocarbon derivatives of the elements of column V are advantageously derived from hydrogen pnictides by total or partial substitution of the hydrogen by monovalent hydrocarbon residues, advantageously with alkyl radicals [in the present description, xe2x80x9calkylxe2x80x9d is used in its etymological sense to be the hydrocarbon residue of an alcohol after removing the alcohol (or -ol) function]; these alkyl compounds will, by analogy with the term pnictide, be denoted in the present description by the term xe2x80x9cpnictines.xe2x80x9d
Thus, in the case of nitrogen, the substitution of hydrogen nitride (ammonia) provides amines, in the case of phosphorus, the substitution of hydrogen phosphide provides phosphines, in the case of arsenic, the substitution of hydrogen arsenide provides arsines and in the case of antimony, the substitution of hydrogen antimonide (or stibide) provides stibines. They are advantageously selected from among the hydrocarbon derivatives of phosphorus, such as the phosphines.
Moreover, the weaker and softer the base, the better and more complete is the exchange. Thus, primary, secondary and preferably tertiary amines provide reactants which contain few HF groups (not more than 5, generally fewer) and which are less powerful than the bases of aromatic heterocyclic type in which the hetero atom, or at least one of the hetero atoms, is selected from column V.
These compounds formed of a base and a distinct number of HF molecules will be designated below by the term xe2x80x9cHF-basexe2x80x9d or xe2x80x9cbase-HFxe2x80x9d complex(es).
The present invention does not feature exchanges with metal fluorides (in particular alkali metal fluorides such as KF, CsF, etc.), which may be expressed by the fact that the amount [(expressed in equivalents) of (alkali metal, ammonium) cation(s)] must be at least equal to once (advantageously at least to 4/3 times, preferably to approximately twice) that of hydrogen in the form of free proton, released halohydric acid or xe2x80x9cbase-HFxe2x80x9d complexes including xe2x80x9cFxe2x80x94(HF).xe2x80x9d
The following empirical rule is presented: if the bases form definite compounds of more than 5 HF per basic function, this is then a powerful reactant capable of exchanging two heavy halogens on the same carbon atom under very mild conditions, and even three under slightly harsher conditions (temperature and pressure). Otherwise, it is a more selective reactant which exchanges, in general, only to provide a single fluorine on a carbon atom under mild conditions and two fluorine atoms on the so-called halophoric carbon under more severe conditions. This invention is especially advantageous for replacing chlorine atoms by fluorine atoms.
Thus, the exchange reactions are essentially successive (in effect, each additional fluorine atom on the halophoric carbon slows the exchange of halogen atoms heavier than fluorine with the latter), thereby making it possible to carry out a selective or complete exchange, by varying the operating conditions and the choice of reactants. As it is generally possible to establish conditions under which the exchange reaction ceases before all of the halogen atoms heavier than fluorine have been replaced thereby, it follows that twofold selectivity is possible. On the one hand, it is possible to exchange only a limited number of halogen atoms heavier than fluorine and, on the other, it is also possible to treat an already partially fluorinated mixture and to significantly modify only the molecules which have not attained the desired number of fluorine atoms.
In general, the ease of exchange of a halogen atom heavier than fluorine with the latter increases with its atomic number.
As is apparent, the stoichiometry and the stoichiometric excess may be varied in order to limit the number of halogen atoms exchanged per molecule.
There may exist several halophoric carbon atoms per molecule. It is preferable for two halophoric atoms not to interfere with each other. A typology of carbon atoms, or even of molecules, most likely to exchange their heavy halogens with fluorine under the influence of the above reactants will be given below. Each characteristic set forth below enhances the benefits of the invention for said carbons.
Thus, it is particularly preferred for the possible residual bond of the halophoric carbon atom advantageously to be a bond with a substituent group selected from among groups which are electron-withdrawing by means of an inductive effect. The said group selected from among the electron-withdrawing groups is advantageously a halogen.
In order to attain good reactivity, it is preferable that the sum of the number of atoms of the said chalcogen(s) to be at least equal to 10. In other words, if there is only one chalcogen, it is preferable for it to be a chalcogen heavier than oxygen. It is particularly advantageous when at least one of the chalcogens is a sulfur atom.
It is particularly preferred that said halophoric carbon bears at least two halogen atoms of atomic number higher than that of fluorine.
Thus, as will later be seen, it is particularly advantageous that said halophoric carbon be trihalomethyl, namely, when it bears three halogen atoms advantageously selected from between chlorine and fluorine.
Regarding said chalcogen(s), it should be appreciated that it is preferably divalent (oxidation number=xe2x88x922) when it is alone, and, when there are two, at least one of them is divalent, the other possibly being simply electron-withdrawing, on account, for example, of donor-acceptor type bonding between the said chalcogen [with the condition, of course, that it is not oxygen, for obvious chemical reasons] and oxygen (for example sulfone or sulfoxide).
Thus, to summarize the above, suitable substrates include molecules having the formula (I):
Rxe2x80x94CXXxe2x80x2xe2x80x94Y(O)rxe2x80x94R5xe2x80x83xe2x80x83(I)
wherein R is a hydrocarbon residue, a halogen, an electron-withdrawing group or a hydrocarbylchalcogenyl group such as an alkoxyl or aryloxy radical, or the sulfur, selenium or tellurium counterparts thereof; X and Xxe2x80x2, which may be identical or different, are each a halogen, preferably chlorine (with the proviso that R, X and Xxe2x80x2 cannot simultaneously be fluorine and that at least one of them is a halogen heavier than fluorine which is to be exchanged with fluorine); Y is a chalcogen, advantageously from an atomic row higher than oxygen, in particular when R is other than hydrocarbylchalcogenyl and with the proviso that, when Y is oxygen, r is equal to zero; r is zero or an integer selected from between one and two and is advantageously less than 2; and R5 is any radical, advantageously a hydrocarbon radical.
When the radical R bears no divalent chalcogen (namely, one in which the two doublets are available), it is preferable for r to be less than two, preferably equal to zero.
When R5 is electron-withdrawing, especially via mesomeric effect, it should be appreciated that the exchange is more difficult, especially for the third fluorine atom on the same carbon.
Thus, for complete exchange, it is desirable that said chalcogen be linked via its second bond to an atom which is electron-donating via an inductive or mesomeric effect. Said electron-donating atom may be another chalcogen (which is a donor via a mesomeric effect), advantageously from an atomic row higher than that of oxygen.
The electron-donating atom may also be a carbon atom of an alkyl radical, or of an electron-rich aryl radical. In this event, the alkyl is advantageously an aralkyl radical, preferably a benzyl radical, and the electron-rich aryl radical is advantageously a five-membered heterocyclic radical or six-membered homocyclic radical.
Thus, for an exchange providing three fluorine atoms on the same halophoric carbon atom, it is preferable for R5 to be alkyl, namely, for its attachment bond to be carried by an sp3-hybridized carbon; advantageously, said sp3-hybridized carbon bears substituents which overall constitute a non-withdrawing or weakly withdrawing moiety (i.e., less withdrawing than dichlorophenyl). Preferably, said sp3-hybridized carbon atom bears at least one and advantageously two hydrogen atoms.
The reaction may proceed when R is equal to H, when at least one of the following two conditions is satisfied:
(i) the reactant is a powerful reactant (i.e., if the bases form specific compounds containing more than 5 HF per basic function);
(ii) it is preferable for the sum of the atomic numbers of the chalcogen(s) to be at least equal to 10.
However, in general, even so, this value Rxe2x95x90H is not preferred.
R5 advantageously is, in particular:
(a) optionally substituted aryl, in particular heteroaryl;
(b) alkyl and in particular:
xe2x80x94CRxe2x80x2Rxe2x80x3xe2x80x94Ar;
wherein Rxe2x80x2 and Rxe2x80x3, which may be identical or different, are each hydrogen, or an aryl or lower alkyl radical (namely, having from 1 to 4 carbon atoms) and, preferably, one or both are advantageously hydrogen; and Ar is a radical having at least one double bond and in which the carbon atom from which the double bond depends is an sp1 carbon and preferably an sp2 carbon. Ar is advantageously a lower aryl, preferably having not more than 10 carbon atoms and advantageously being homocyclic;
xe2x80x94CRxe2x80x2Rxe2x80x3xe2x80x94CR1R2xe2x80x94EWG;
wherein the radicals Rxe2x80x2 and Rxe2x80x3 are as defined above; EWG is an Electron-Withdrawing Group, a group which stabilizes a double bond or a leaving group; and R1 and R2, which may be identical or different, are each a hydrogen or halogen atom, or a hydrocarbon radical, in particular an alkyl, alkyne, alkene or aryl radical; one or both are advantageously hydrogen atoms.
Each radical R and R5 typically contains not more than 30 atoms (of which not more than 20 are carbon atoms), advantageously 20 atoms (of which not more than 15 are carbon atoms), and preferably not more than 15 carbon and/or nitrogen atoms (of which not more than 12 are carbon atoms). The total number of carbons in the substrate molecules only rarely is greater than 50, and advantageously is not more than 30.
When R5 is aryl, particularly exemplary are those compounds in which:
R is lower alkyl [optionally substituted, and in particular halogenated (including perhalogenated and in particular perfluorinated)], halogen, aryl or Arxe2x80x2Oxe2x80x94 and Arxe2x80x2Sxe2x80x94, in which Arxe2x80x2 is a lower aryl (namely, containing not more than 10 carbon atoms);
R5 is an optionally substituted phenyl radical, an optionally substituted heterocycle, advantageously a five-membered heterocycle, preferably one containing two hetero atoms (it is desirable to have two nitrogen atoms); thus, for example, the radical xe2x80x94Y(O)rxe2x80x94R5 advantageously corresponds to the formula: 
wherein n has the same values as r, namely 0, 1 or 2; R11 and R12, which may be identical or different, advantageously in the ortho position, are each hydrogen or a halogen; R13, advantageously in the para position, is a halogen, an alkyl group optionally substituted by one or more halogen atoms (including a group selected from among the perfluoroalkyl radicals), an alkyloxyl group optionally substituted by one or more halogens (including a group selected from among perfluoroalkyloxyl radicals), or an SF5 radical; Xxe2x80x3 is a nitrile function or a halogen atom; and R15 is an amino group, optionally mono- or disubstituted with radicals (the same or different, in the case of disubstitution) selected from among alkyl radicals optionally substituted by one or more halogens (including perfluoroalkyl radicals), acyl radicals optionally substituted by one or more halogens (including perfluoroacyl radicals) or alkyloxycarbonyl radicals.
The alkyl, alkyloxyl and acyl radicals are preferably light or lower, i.e., they contain not more than four carbon atoms.
It should be appreciated that when R13 is an alkyloxyl group optionally substituted by several halogen atoms and when at least one of said halogen atoms is from an atomic row higher than that of fluorine, there are two possible carbon centers of exchange.
The residues R5 and R may constitute one and the same radical, but this being a divalent radical. For example, they may together form an aryl radical, the points of attachment being borne either by two carbons on the same ring and in a vicinal position to each other; or by two carbons beta to each other, not belonging to the same ring, but the two rings of which are fused and condensed (e.g., the instance of two alpha positions of naphthalene or equivalents); or by two carbons xcex3 to each other belonging to rings separated by a third ring, in the manner of phenanthrene.
By way of examples of such formulae, the following are presented:
Vicinal carbons on the same ring: 
with the proviso that Yxe2x80x2 can be either a single bond or a chalcogen (with the same preferences as Y), or a methylene radical optionally mono- or disubstituted with halogens, or a divalent group xe2x80x94Yxe2x80x3xe2x80x94CEExe2x80x2 or xe2x80x94CEExe2x80x2xe2x80x94Yxe2x80x3xe2x80x94, with the further proviso that Yxe2x80x3 can have the same definition as Y, and E and Exe2x80x2 the same values as X and Xxe2x80x2, respectively (E and Exe2x80x2 may simultaneously be fluorine); R6 and R7 are each, independently, hydrogen, a halogen, a nitro group, a nitrile, a hydrocarbon group, advantageously having not more than 5 carbon atoms, an alkyl group optionally substituted by one or more halogen atoms (including a group selected from among the perfluoroalkyl radicals), an alkyloxyl group optionally substituted by one or more halogen atoms (including a group selected from among the perfluoroalkyloxyl radicals), or an SF5 radical.
And, in particular: 
Carbons on two separate rings with R8 having the same values as R6 or R7: 
In a preferred embodiment of the invention, cleavages (or lyses) may be carried out in order to form compounds which are particularly useful for organic synthesis and for the synthesis of chalcogenophoric acids (and in which the chalcogen is from a row at least equal to that of sulfur). The oxidation of the compounds according to the invention may be carried out using peroxides and, in particular, those of hydrogen (aqueous hydrogen peroxide solution and various hydroperoxides [for example acyl hydroperoxides and alkyl hydroperoxides]) under conditions which are per se known to this art, or by halogens and in particular chlorine. In this embodiment, it is often advantageous for the chalcogen to be sulfur and for it to include a subsequent step of oxidation of said sulfur atom. The oxidation step is advantageously carried out in order to obtain said sulfur atom in the form of a sulfone. The oxidation may also be carried out in order to obtain said sulfur atom in the form of a sulfoxide, of a sulfenate, or in an equivalent oxidation state.
This embodiment may subsequently include a downstream step of hydrolysis, advantageously in an alkaline medium, to provide a corresponding sulfinic or sulfonic acid salt.
This type of reaction may produce, according to the particular reaction conditions, either sulfenyls or sulfoxides, or, lastly, as indicated above, may include lyses to produce sulfonic or sulfinic acids, or equivalents thereof when the chalcogen is selenium or tellurium instead of sulfur.
In addition, it has now surprisingly been determined that if only the stoichiometric amount or a slight stoichiometric excess is used (amount of halogen ranging from 0.5 to 1.5 SA, advantageously from 8 to 1.3, preferably from 0.9 to 1.2 SA), sulfenates whose carbon vicinal to the sulfur is perfluorinated produce the sulfinyl halide when they are oxidized with halogen atoms (advantageously chlorine).
The halogenation is carried out by subjecting the sulfenate, advantageously diluted in a very non-polar (i.e., unable to dissolve more than 5% mass of water), essentialy anhydrous (i.e., where the content in water repesents at most ⅓ in mole of the substrate, advantageously at most ⅕, preferably at most {fraction (1/10)}) and chlorine-insensitive solvent, to the action of chlorine in an at least substantially stoichiometric amount, at a temperature at most equal to 100xc2x0 C., advantageously ranging from 0xc2x0 C. to 50xc2x0 C.
The subject reaction can be represented as follows: 
This reaction is of particular interest for the radicals R containing not more than 10 carbon atoms. It proceeds all the better the more stable the carbocation R5+; thus, for the latter reaction, R5 is advantageously benzylic, allylic or tert-alkyl. Hence, among the appropriate substrates are those of formula II, wherein Y is sulfur or a higher chalcogen and r is equal to 1 and oxygen is advantageously intercalated between Y and CRxe2x80x2Rxe2x80x3.
It will be appreciated that the halides, and in particular sulfinyl chlorides (of type Rxe2x80x94CF2xe2x80x94SOxe2x80x94) are particularly important synthetic intermediates.
Molecules which are particularly suitable for this reaction are especially those of formula (II), derived from the formula I:
Rxe2x80x94CFXxe2x80x94Y(O)rxe2x80x94CRxe2x80x2Rxe2x80x3xe2x80x94Arxe2x80x83xe2x80x83(II)
wherein R is a halogen, electron-withdrawing group, hydrocarbyl radical such as an alkyl or aryl radical, or a hydrocarbylchalcogenyl radical such as an alkoxyl or aryloxyl radical, and the sulfur, selenium and tellurium counterparts thereof; X is a halogen, preferably chlorine and especially fluorine; Y is a chalcogen, advantageously from an atomic row higher than oxygen and with the proviso that, when Y is oxygen, r is equal to zero; r is zero or an integer selected from between one or two; Rxe2x80x2 and Rxe2x80x3, which may be identical or different, are each an aryl or lower alkyl radical, or preferably, one or both are hydrogen atoms; and Ar is a compound having at least one double bond and in which the carbon atom from which the double bond depends is an sp1 carbon and preferably an sp2 carbon. Ar is advantageously a lower aryl radical, preferably having not more than 10 carbon atoms and advantageously being homocyclic.
In another preferred embodiment of the present invention, the compounds of formula: 
are subjected to a xcex2-elimination. In the formula immediately above, one, advantageously at least two, of the radicals Rxe2x80x2, Rxe2x80x3, R1 and R2 is a hydrogen atom (it is desirable for one of the radicals on each of the xcex1 and xcex2 carbons to be hydrogen); and EWG is an Electron-Withdrawing Group, a group which stabilizes a double bond, or a leaving group (in the event that it is desired to form, by xcex2-elimination with cleavage between the xcex2 carbon and the EWG, a derivative of the formula xe2x80x94CFXxe2x80x94Y(O)rxe2x80x94CRxe2x80x2Rxe2x80x3xe2x95x90CR1R2).
Electron-withdrawing groups which are exemplary are halogen atoms, groups containing a carbonyl function (such as amides, esters, ketones and aldehydes), groups derived from a carbonyl function (such as imines, amidines, oximes, thioketones, thioesters, thioamides and thioloesters), nitriles, pnictoniums (in particular phosphoniums and ammoniums; see below), the nitro group, ortho esters, radicals in which at least the atom vicinal to the free bond (or open bond, i.e., the bond which links the radical to the remainder of the molecule considered) is perhalogenated and, in particular, perfluorinated; thus, perfluoroalkyl radicals such as trifluoromethyl and pentafluoroethyl are suitable, as are 1,1-difluoro radicals and 1,1,2,2-tetrafluoroalkyl radicals, such as 1,1-difluoroethyl, 1,1-difluoro- and 1,1,2,2-tetrafluoropropyl.
Other electron-withdrawing groups include groups derived from oxygenated chalcogens (such as sulfoxides and sulfones), or from elements of column VB of the Periodic Table such as phosphine oxides and phosphonic or phosphinic acid esters; the free bond is advantageously borne by the metalloid (chalcogen or element from column VB).
Again in the event of xcex2-eliminations, exemplary leaving groups, other than the halogens indicated above, include the pseudohalogens as described below. A xe2x80x9cpseudohalogenxe2x80x9d is considered to be a radical (in general this radical comprises a light chalcogen (sulfur or preferably oxygen) via which it is bonded to the remainder of the molecule) which, on leaving, forms an anion whose associated acid has an acidity (measured by the Hammett constant) at least equal to that of acetic acid. Among the typical pseudohalogens which are exemplary are the acyloxyl radicals corresponding to the acids perhalogenated in the alpha-position of the acyloxyl function, such as trifluoroacetoxy (CF3xe2x80x94COxe2x80x94Oxe2x80x94), and especially sulfonyloxyl radicals, especially those in which the carbon bearing the sulfur is perfluorinated, an example of which is trifluoromethanesulfonyloxy (CF3xe2x80x94SO2xe2x80x94Oxe2x80x94).
According to the present invention, those pseudohalogens which, on leaving, have an acidity at least equal to that of sulfonic acids, such as tosyl (example of arylsulfonic acids), or mesyl (example of alkylsulfonic acids) are preferred.
Consistent herewith, a pnictonium is a tertiary pnictine quaternized with a hydrocarbyl radical (such as an aryl or alkyl radical, including the aralkyl radicals).
Said pnictines are trivalent hydrocarbon derivatives of the elements of column VB of the Periodic table. They are derived from the hydrogen pnictides by total or partial substitution of the hydrogen with hydrocarbon residues which may be bonded to the atom from column VB via a double bond (as in the imines) or a triple bond (as in the nitrites).
However, the hydrocarbon derivatives of the elements from column V are advantageously derived from hydrogen pnictides by total or partial substitution of the hydrogen by monovalent hydrocarbon residues, advantageously by alkyl radicals [xe2x80x9calkylxe2x80x9d is again used in its etymological sense, to be an alcohol hydrocarbon residue after removing the alcohol (or -ol) function]; these compounds derived from pnictide are, by analogy with the term pnictide, denoted in the present description by the term pnictines.
Thus, in the case of nitrogen, the substitution of hydrogen nitride (ammonia) provides amines, in the case of phosphorus, the substitution of hydrogen phosphide provides phosphines, in the case of arsenic, the substitution of hydrogen arsenide provides arsines and in the case of antimony, the substitution of hydrogen antimonide (or stibide) provides stibines. They are advantageously selected from among the phosphorus hydrocarbon derivatives such as phosphines.
In general, it is desirable for the xcex2-elimination to be carried out with cleavage between the Y(O)r and CRxe2x80x2Rxe2x80x3 moieties, in which event at least one of R1 and R2 must be hydrogen and, also in which event, it is preferable for EWG to represent an electron-withdrawing (or attracting) group or a group which stabilizes a double bond. Exemplary groups which stabilize a double bond include those which comprise a bond capable of being conjugated with a possible double bond between the xcex1 and xcex2 carbons; other than the electron-withdrawing radicals containing a double bond indicated above, exemplary such groups include the alkynes, alkenes and aryls.
It is also desirable for EWG to be sufficiently electron-withdrawing to stabilize a carbanion in the xcex2-position; when EWG is aryl and, in particular, an optionally substituted phenyl radical, it is desirable for R1 and/or R2 themselves to be selected from among suitable EWG-containing radicals and, in particular, from alkynes, alkenes and aryls.
Lastly, still in the event of a xcex2-elimination with cleavage between the Y(O)r and CRxe2x80x2Rxe2x80x3 moieties, it is desirable for EWG to be a mediocre leaving group and advantageously one which is not as good a leaving group as Rxe2x80x94CFXxe2x80x94Y(O)r. It is also advantageous for r to be at least equal to 1, preferably at least equal to 2.
The reaction is carried out under conditions and according to techniques per se known to this art, using strong bases whose pKa of the associated acid is advantageously at least equal to 14.
To determine the conditions for any particular reaction, empirical rules which may be used in the majority of situations are given below.
As aforesaid, xe2x80x9chydrocarbylchalcogenylxe2x80x9d is a radical of the structure R6xe2x80x94Yxe2x80x3xe2x80x94, wherein R6xe2x80x94 is a hydrocarbon radical, i.e., a radical containing at least hydrogen and carbon and in which the atom from which the bond depends (here with Yxe2x80x3) is a carbon atom, and wherein Yxe2x80x3 is a chalcogen (oxygen, sulfur, selenium or tellurium). R6 is advantageously an alkyl radical [optionally substituted, and in particular halogenated (including perhalogenated and in particular perfluorinated radicals)], or an optionally substituted aryl radical.
The definitions of the radicals are in respect of the formula (I):
Rxe2x80x94CXXxe2x80x2xe2x80x94Y(O)rxe2x80x94R5xe2x80x83xe2x80x83(I)
By the expressions xe2x80x9celectron-donatingxe2x80x9d and xe2x80x9cweakly electron-withdrawingxe2x80x9d are intended as withdrawing as or less withdrawing than a dichlorophenyl function (this definition also being suitable for non-electron-withdrawing aryl). Conversely, by xe2x80x9celectron-withdrawingxe2x80x9d or xe2x80x9csignificantly electron-withdrawing,xe2x80x9d which here have the same meaning, as may be deduced from the above definition, are intended the opposite of xe2x80x9celectron-donating and weakly electron-withdrawing,xe2x80x9d i.e., more withdrawing than a dichlorophenyl function.
One example (more precisely, one paradigm) of the weak reactants (see the above empirical rule) is the compound defined as triethylamine.3 HF.
One example (more precisely, one paradigm) of the strong reactants (see the above empirical rule) is the compound defined as pyridine.10 HF.
Mild conditions: xcex8=melting point at not more than 50xc2x0 C.;
Harsh conditions: 50xc2x0 C. to 100xc2x0 C. (or at the boiling point, if this is lower at the pressure considered);
Very harsh conditions: xcex8=100xc2x0 to 150xc2x0 C. and, where appropriate, pressures above atmospheric pressure;
In the event that, in the formula (I), X and Xxe2x80x2 represent halogens heavier than fluorine, the reaction equations may be expressed as follows:
Reaction Providing a Fluorine Atom on the Halophoric Carbon 
Reactions Leading Providing Two Fluorines on the Halophoric Carbon 
and with R representing a halogen heavier than fluorine
Reactions Providing Three Fluorine Atoms on the Halophoric Carbon 
Compare also the following summary Table I:
In order to further illustrate the present invention and the advantages thereof, the following specific examples are given, it being understood that same are intended only as illustrative and in nowise limitative.